# Ground sampling distance (GSD) in photogrammetry

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The Ground Sampling Distance (GSD) is the distance between two consecutive pixel centers measured on the ground. The bigger the value of the image GSD, the lower the spatial resolution of the image and the less visible details.

The GSD is calculated based on:

• The flight height / the distance from the terrain or object (H).
• The camera specifications:
• Image width (ImW).
• Sensor width (SW).
• Focal length (F)

Flight height (H) and camera specifications (ImW, SW, and F) influence the GSD.

Information:

It is important to decide on the GSD value before starting the image acquisition in order to adjust the flight height and the camera specifications to the project requirements. For example, when a detailed reconstruction of the area is needed, we recommend flying closer (low GSD) to the object of interest. On the other hand, when covering large areas that do not need very detailed results, flying higher (high GSD) can greatly reduce the acquisition time and batteries needed as well as reduce the processing time.

Example:
• A GSD of 5 cm means that one pixel in the image represents linearly 5 cm on the ground (5*5 = 25 square centimeters).
• A GSD of 30 cm means that one pixel in the image represents linearly 30 cm on the ground (30*30 = 900 square centimeters)
 Orthomosaic with a GSD of 5 cm - more detailed. Orthomosaic with a GSD of 30 cm - less detailed.

Note: Even when flying at a constant height, the images of a project may not have the same GSD. This is due to terrain elevation differences and changes in the angle of the camera while shooting. Since the orthomosaic is created using the 3D point cloud and the camera positions, an average GSD will be computed and used.

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### Article feedback (for troubleshooting, post here instead)

• Pritpal Singh

Team Pix 3D, do we have a Three D block of GSD so I can place it dynamically under flight planning. means SW | DW as 3d like the one visible in Pix4D after the flight. i guess it will really help develop failsafe missions

• Gaël (Pix4D)

Hi Pritpal,

If my understanding is correct you would like to have a visual display of the image footprint while planning a mission using Pix4Dcapture?
Note that the most important parameter when flying is the GSD which you can have an estimate while planning the mission with Pix4Dcapture. Also to process properly your data, the other important parameter to consider is the overlap which you can also set in Pix4Dcapture.

Best,

• Sara Heshmati

Hi,

How do I get the resolution of my pictures using the GSD (if that makes sense)? For example, I have a GSD of 3.5 cm/ pixel.

• lala lula

Hi Sara..................simple use the calculator

• Hernán Guzmán

Hello, I would like to know, if the height of the terrain changes, what is the variation of the gsd allowed?

• Marco Paccagnella